1. Field of the Invention
The present invention relates to improved polyester articles. Specifically, the present invention relates to a polyester article exhibiting a generally hydrophilic surface.
2. Description of the Related Art
The use of various polyester compositions for forming a variety of shaped articles is known. For example, polyesters are known to be useful in forming fibers which can be formed into a variety of woven and nonwoven materials. Such polyester materials generally possess a relatively hydrophobic surface. When it is desired to employ a woven or nonwoven material in an absorbent product such as a diaper, bandage, adult incontinent product, feminine napkin, or the like, it is often desirable that such material exhibit a generally hydrophilic (wettable) surface in order to allow water to pass therethrough.
In the past, when it has been desired to employ a woven or nonwoven polyester material in a personal care product, for other than the backing material, it has been suggested to render the polyester material wettable (hydrophilic) by applying a surface treatment such as a surfactant to the polyester. Unfortunately, such surface treatments are generally fugitive in nature. That is, while appearing wettable for an initial application of liquid, after a given amount of water has passed through the polyester material, the surface treatment tends to wash off of the polyester material. Obviously, after the surface treatment has been washed off the polyester material, the polyester material is no longer capable of exhibiting a wettable (hydrophilic) surface and instead exhibits its natural hydrophobic surface.
When polyester materials are employed in personal care products, such as diapers, it is likely that they will be required to pass relatively large quantitie of liquid waste and will be subjected to multiple insults of liquid waste. When polyester fabrics having a surfactant type surface treatment are employed in a diaper, they are generally capable of passing at least the first urine insult but become less capable of passing urine with each subsequent insult. Since a diaper may generally be subjected to three or more urine insults, surfactant treated polyester materials have proven generally unsatisfactory for use in diapers, for example, as a body-side liner.
Accordingly, attempts have been made to develop a surface treatment for polyester materials which surface treatment is generally not fugitive thereby rendering said polyester fiber wettable on a more permanent basis. For example, U.S. Pat. No. 3,416,952 issued Dec. 17, 1968 to McIntyre et al., is directed to a surface modifying treatment for shaped articles made from polyesters. Described is a process for treating shaped articles made from an essentially linear crystalizable polyester. The polyester article is treated with a polymeric compound which contains, within a single molecule, repeat units identical with those forming the crystalizable portions of the polyester article and at least one active group serving to modify the surface of the shaped article. Described as being suitable for use as an active group are water solvatable polymeric groups. According to the process, the polymeric compound is applied to the surface of the shaped article and the shaped article subjected to a thermal treatment at a temperature above 90.degree. C. In order to prevent damaging the shaped article the thermal treatment generally occurs at a temperature below the melting point of the shaped article. The shaped article so produced is described as appearing generally hydrophilic in nature.
Similarly, U.S. Pat. No. 4,376,013 issued Mar. 8, 1983 to Wang is directed to a process for removal of pitch-containing water and method of coating belts for paper machines. Disclosed is a method of treating papermakers' forming and press belts made from polyethylene terephthalate mono or multi filament yarns. The belts are coated with a coating compound which is co-crystalline with the polyethylene terephthalate at the surface of the filament. The coating contains a profusion of oxyalkylene groups to establish a hydrophilic barrier of active oxyalkylene groups by solvation with water to repel the pitch from the belt. Disclosed as a suitable coating is a block or graft copolymer in which the first polymeric constituent is a crystalline polyester and the second polymeric constituent is solvatable by water. After the coating is applied to the polyester belt, the belt is raised to a temperature within the range of from about 250.degree. F. to about 420.degree. F. (about 121.degree. C. to about 216.degree. C.). The heat treatment is described as causing co-crystallization of the coating compound which has polyester repeat units identical with those of the repeat unit constituting the crystallized segment of the internal structure of the filament.
Both of the above references describe applying a surface coating to polyesters and heating the coated polyesters to temperatures less than the melting point of the polyesters. Polyester articles produced as described in the above two patents may have surface treatments which are generally less fugitive than surfactant treated polyesters. Nonetheless, it has been found that such surface treatments do, under certain circumstances, tend to be fugitive and wash off of the polyester articles. This is particularly true when the active groups responsible for imparting the hydrophilic nature to the polyester articles possess a high degree of hydrophilicity. In such cases, due to the high degree of hydrophilicity displayed by the active groups, the attraction of the hydrophilic groups for water is sufficient to cause the nonhydrophilic portion (e.g., polyester portion) to be pulled from the polyester article.
Additionally, certain polyesters and polyester formed into certain shapes have limited dimensional stability. For example, many polyesters, when formed into meltblown webs, will be dimensionally stable only up to a temperature of about 80.degree. C. Thus, to employ the heat treatment processes described in the referenced two patents at temperatures significantly above about 80.degree. C. will cause the meltblown webs to contract into "nuggets" of polyester if the meltblown webs are unrestrained.
Finally, the process described in the above cited two patents requires separate heating chambers and processing conditions sufficient to allow the articles to be maintained at an elevated temperature for a given period of time. This is costly in terms of equipment, energy and efficiency.